<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .red{
            width: 100px;
            height: 100px;
            background-color: red;
            float:left;
        }
        .blue{
            width: 200px;
            height: 200px;
            background-color: blue;
            float: left;
            text-align: center;
            line-height: 200px;
        }
        .green{
            width: 300px;
            height: 300px;
            background-color: green;
            text-align: center;
            line-height: 100px;
        }
    </style>
</head>
<body>
    <div class="red">红色</div>
    <div class="blue">蓝色</div>
    <div class="green">绿色</div>
</body>
</html>